Valve arrangements of the indicated type are being increasingly designed as valve modules permitting acquiring a certain number of special alternative embodiments, in addition to implementation of standard alternative embodiments. Generally these special alternative embodiments increase the construction effort for producing the alternative embodiment itself using the installation space available within the standard valve module.
One typical case for electrically controlled valves is the desire of the user to be able to execute a pressure switching function or independently operated switching functions, besides controlling the directional control valve. For example, the function of “quantitative cutoff” is desired in which by pressure limitation in the control of a section compensator the control cross section of the compensator in the inflow to the slide diaphragm of the directional control valve is closed. Currently solutions are possible in which these valves are offered with setscrews for maximizing and setting inflow pressure to the two consumer connections (pipe connections) A and/or B. The setscrews are generally adjusted by hand and are accompanied by interruptions in operation on the machine.
Electrical adjustment by setting a potentiometer would be a desirable improvement. In the prior art, mobile directional control valves are known implementating such an electrical adjustment function, but require three proportional magnets taking up much installation space on the pertinent machine. Furthermore, there are additional wiring costs for implementation of the required bus hardware.
EP 0 935 713 B1 discloses a valve arrangement for actuating a consumer with a directional control valve continuously adjustable and acting as an inflow throttle, via which a pump connection can be connected to the consumer connections A, B. The respective consumer is connected to the directional control valve via working lines. In each working line there is a throttle to set the volumetric discharge flow of hydraulic oil by the consumer. In the known solution one control side of the throttle and one control side of the directional control valve at a time are each connected to one control unit at a time by a control channel. By two control units, the control pressures in the two control channels are adjustable independently of one another. When the inlet volumetric flow is set the two control pressures are greater than zero and the discharge-side throttle means can be completely opened independently of the valve slide position of the directional control valve, a valve arrangement is then devised in which with minimized hardware cost the energy losses can be minimized in the discharge from a consumer. The hydraulic volumetric flow is set by the directional control valve acting as an inflow throttle.
The throttle in the known solution also has two return throttles, each assigned to a consumer connection A or B. Each of these return throttles is provided with a tank connection T. A permanent connection is between the return throttles and the actuating pressures xa, xb, respectively, acting as an actuating pressure in the opposite direction on the control slide with the inflow diaphragm of the directional control valve. This directional control valve does not have a tank connection T in this regard. For this known solution, in addition to the control slide of the directional control valve, the respective return throttle is controlled by a total of two proportional magnets independent of one another and making available the indicated control pressures xa, xb. This known valve arrangement combined into a valve block is relatively large.
DE 10 2005 050 169 A1 discloses an LS control arrangement with a directional control valve having a valve slide. When the valve slide is set in one direction, a first consumer connection A is connected to inflow connection P and the second consumer connection B is connected to discharge connection T. When the valve slide is set in the other direction, second consumer connection B is connected to one inflow connection P and other consumer connection A is connected to a discharge connection T. By the inflow control edge, the opening cross section of an inflow metering orifice is determined and in turn is assigned an individual compensator for keeping the pressure drop constant over the inflow metering orifice. With an LS control oil flow path via which the load pressure can be tapped downstream from the inflow metering orifice and can be reported through the valve slide into the LS control chamber of the directional control valve, a maximum pressure in the LS control oil flow path is limitable by a pressure limitation valve. In that in the known solution the LS control oil flow path during setting of the valve slide in one direction in succession or overlapping can be connected to two pressure limitation chambers to which one pressure limitation valve at a time can be assigned for LS pressure limitation, multistage inflow pressure limitation is possible. The load pressure also can be limited to different values in different stroke ranges of the valve slide. This ability is advantageous for certain tasks in mobile machinery. Continuous adjustment processes are, however, not possible with the known solution.